Open AccessMechanistic Investigation of the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates from Allylic Alcohols
Author(s) -
Johanna M. Larsson,
Kálmán J. Szabó
Publication year - 2012
Publication title -
journal of the american chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.115
H-Index - 612
eISSN - 1520-5126
pISSN - 0002-7863
DOI - 10.1021/ja309860h
Subject(s) - transmetalation , chemistry , allylic rearrangement , borylation , silanes , palladium , silylation , catalysis , stereoselectivity , organic chemistry , hydroboration , medicinal chemistry , photochemistry , alkyl , silane , aryl
The mechanism of the palladium-catalyzed synthesis of allylic silanes and boronates from allylic alcohols was investigated. (1)H, (29)Si, (19)F, and (11)B NMR spectroscopy was used to reveal key intermediates and byproducts of the silylation reaction. The tetrafluoroborate counterion of the palladium catalyst is proposed to play an important role in both catalyst activation as well as the transmetalation step. We propose that BF(3) is generated in both processes and is responsible for the activation of the substrate hydroxyl group. An (η(3)-allyl)palladium complex has been identified as the catalyst resting state, and the formation of (η(3)-allyl)palladium complexes directly from allylic alcohols has been studied. Kinetic analysis provides evidence that the turnover limiting step is the transmetalation, and insights into notable similarities between the borylation and the silylation reaction mechanisms enabled us to considerably improve the stereoselectivity of the borylation.